(27d) New Performance Indicators for Adsorbents Used in CO2 Capture Swing Adsorption Processes

As adsorption process has increasingly received attention in CO₂ capture area, a number of studies have suggested a variety of adsorbents such a metal-organic frameworks (MOFs), zeolitic imidazolate frameworks (ZIFs) and many modified versions of conventional adsorbents. However, because of their limited scope of the studies, they have evaluated their adsorbents by using conventional performance indicators: working capacity and selectivity. The performance indicators rarely consider the situation of the adsorbents' practical application in the adsorption process. In order to evaluate the adsorbents with the consideration of their eventual application, e.g., pressure swing adsorption (PSA) process, dynamic simulations with a rigorous model of the adsorption process are needed, but the simulations cannot be carried out conveniently by the developers of new adsorbents. Furthermore, the high computation cost caused by the nonlinearity and cyclic operation of the PSA system hinders the evaluation of adsorbentsâ?? suitability for their process-level application. For those reasons, this work derives simple formulas for the process-level performance of an idealized PSA system. The efficiency and the CO₂ purity of produced gas in the idealized PSA system are defined as performance indicators for the evaluation of a target adsorbent. For further simplicity, the performance indicators are derived in the explicit form of an analytic solution. The derived explicit equations are suggested as formulas of the new performance indicators for the evaluation. With the formulas, the performance of a target adsorbent in the PSA process can be obtained with simple calculation only from lab-scale measurement data such as adsorption isotherm data. Because the suggested formulas are based on the idealized PSA process where the theoretically maximum performance of each adsorbent is achieved, the suggested way is fairer than comparing the simulations of different adsorbents with some prior design and operating conditions which may be preferred by particular adsorbents. In order to show the usefulness of the formulas, a case study involving several real adsorbents is presented. The results from the formulas about the new indicators are then compared both to the simulation results of a rigorous dynamic model and to the conventional performance indicators.

Acknowledgement: The authors would like to acknowledge the financial support from the grant (G01160051) funded by Saudi Aramco-KAIST CO2 management center.